using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

namespace NHCourse
{
   public static class ExtensionMethods
   {
      public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string property)
      {
         return ApplyOrder(source, property, "OrderBy");
      }

      public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, string property)
      {
         return ApplyOrder(source, property, "OrderByDescending");
      }

      public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string property)
      {
         return ApplyOrder(source, property, "ThenBy");
      }

      public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, string property)
      {
         return ApplyOrder(source, property, "ThenByDescending");
      }

      public static string GetPropertyName<T, U>(this T source, Expression<Func<T, U>> exp)
      {
         return ((MemberExpression)exp.Body).Member.Name;
      }

      public static string GetPropertyName<T, U>(this IEnumerable<T> source, Expression<Func<T, U>> exp)
      {
         return ((MemberExpression)exp.Body).Member.Name;
      }

      private static IOrderedQueryable<T> ApplyOrder<T>(IQueryable<T> source, string property, string methodName)
      {
         string[] props = property.Split('.');
         Type type = typeof(T);
         ParameterExpression arg = Expression.Parameter(type, "x");
         Expression expr = arg;
         foreach (string prop in props)
         {
            // use reflection (not ComponentModel) to mirror LINQ
            PropertyInfo pi = type.GetProperty(prop);
            expr = Expression.Property(expr, pi);
            type = pi.PropertyType;
         }
         Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
         LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);

         object result = typeof(Queryable).GetMethods().Single(
            method => method.Name == methodName
                      && method.IsGenericMethodDefinition
                      && method.GetGenericArguments().Length == 2
                      && method.GetParameters().Length == 2)
            .MakeGenericMethod(typeof(T), type)
            .Invoke(null, new object[] {source, lambda});
         return (IOrderedQueryable<T>)result;
      }
   }
}